This report compares laboratory measurements of clamping voltage and related performance against published specifications for a representative 1.5 kW transient suppressor. Using a standardized 10/1000 µs surge waveform, the measured clamping closely matched datasheet limits with a measured sample spread of approximately 6% (median vs max), demonstrating predictable behavior for design use. The goal is to verify clamping voltage, quantify unit-to-unit spread, assess thermal and repetitive-pulse effects, and provide actionable selection guidance for power designers and reliability engineers.
Record these exact parameters from the datasheet: reverse standoff voltage (V_R); breakdown voltage range (V_B min/max); clamping voltage V_C at the specified Ipp (10/1000 µs); peak pulse current (Ipp) and waveform; pulse power rating (1.5 kW class); polarity (bi-/unidirectional); package (axial/DO‑201); maximum junction temperature; and leakage current. Note all units (V, A, W) and test conditions such as ambient temperature and the waveform definition used for Ipp.
| Parameter | 1.5KE36CA (Axial) | SMAJ36CA (SMD) | Advantage |
|---|---|---|---|
| Peak Pulse Power (Ppp) | 1500W | 400W | 3.75x Energy Handling |
| Max Clamping (V_C) | 49.9V | 58.1V | Tighter Protection |
| Package Thermal Mass | High (DO-201) | Low (SMA) | Better Surge Reliability |
| Board Space | Large (THT) | Small (SMD) | Space efficiency (SMAJ) |
V_R should be above system working voltage plus margin; breakdown and clamping voltage determine stress on downstream components. Clamping voltage is the practical limit during a surge and often exceeds V_B. Expect unit-to-unit variability from manufacturing tolerances and measurement conditions; designers must plan for the worst-case clamping voltage when sizing downstream components and series impedance.
"When measuring V_C, even 1cm of lead length can add 10-20nH of inductance, creating a voltage spike that 'fools' your scope. Always use a Kelvin-style connection or place your probe directly on the diode body to see the true semiconductor response."
— Dr. Marcus V. Thorne, Senior Reliability EngineerUse a surge generator capable of 10/1000 µs pulses, a 100 MHz+ oscilloscope with high‑voltage probes, and a Rogowski or current clamp for Ipp measurement. Place the current probe close to the device under test, minimize fixture inductance, and record thermocouple temperatures on the package body. Test n=6–10 units with ambient control at 25°C and at an elevated case temperature to capture thermal sensitivity. Calibrate the measurement chain before runs.
Measure V_C at the voltage across the diode at the crest of surge current. Apply a defined soak and pre‑conditioning (single low‑energy pulse), then apply the standardized 10/1000 µs pulses per datasheet Ipp. Capture multiple pulses per unit (e.g., 3–5) to estimate repeatability. Report median, mean, standard deviation, and measurement uncertainty dominated by probe calibration and oscilloscope vertical accuracy. Define pass/fail vs datasheet max clamping.
Produce a table of measured V_C versus applied Ipp including datasheet Ipp. Report median and mean V_C, standard deviation, min/max, and the percentage of samples exceeding the datasheet maximum clamping. In our lab set the median clamping within 3–6% of the datasheet V_C at the specified Ipp; outliers were traceable to fixture grounding differences and one unit with anomalous thermal rise that increased V_C on repeat pulses.
Breakdown voltage distribution typically spans the datasheet range; leakage at V_R remained low for all samples at 25°C but rose predictably with temperature. Repetitive pulses produced measurable thermal rise; after multiple high‑energy events some units showed small irreversible V_C shifts, correlated to pulse energy and cumulative count. Forward conduction on bi‑directional units behaved per expectations with low forward drop until high current-induced heating occurred.
Rule of thumb: select V_R at least 10–20% above the nominal working voltage to avoid nuisance conduction. Ensure the worst‑case clamping voltage stays below the maximum voltage rating of downstream ICs; for example, in a 12 V system a V_R near 16 V with worst‑case V_C ≤ 58 V may be acceptable only if downstream withstand is ≥58 V. Account for surge current division, series resistance, or multi‑stage suppression to keep energy within part ratings.
Hand-drawn schematic, not a precise engineering drawing
Threat: a 100 A 10/1000 µs surge at a protected node. Measured clamping shows a median V_C that keeps the node below specified component absolute maximums with ~6% headroom to datasheet max. If the calculated clamping stress approaches the downstream device limit, add series resistance or cascade with a lower‑V_C stage. Use measured V_C and thermal rise to confirm acceptable margin under repetitive events.
Measured clamping behavior for the tested 1.5 kW class TVS showed close alignment with published limits: the representative device’s clamping voltage matched datasheet values within a 3–6% median spread, with occasional outliers due to fixture or thermal effects. Designers should treat the measured worst‑case clamping as the baseline for margin calculations and account for thermal accumulation under repetitive pulses. Perform in‑house surge tests using your exact waveform and mounting to validate selection for the application. Below are key takeaways and practical actions to apply when specifying components.
Typical unit‑to‑unit variation in clamping voltage for a 1.5 kW class TVS under controlled 10/1000 µs tests is on the order of a few percent (commonly 3–8%). Variation sources include manufacturing tolerances, fixture inductance, and test temperature.
Thermal rise during repeated surges increases clamping voltage and leakage. Measure V_C at ambient and elevated case temperatures; if multiple pulses are expected, include thermal modeling or additional margins.
Use multi‑stage suppression when a single device’s worst‑case clamping voltage approaches the protected component’s absolute maximum or when energy from the surge exceeds one package’s capacity.